Current air classifiers separate the heavy fraction from a light fraction by using an air curtain to blow the lighter fraction over a gap while the heavier falls down through the gap prior to a receiving surface for the lights, which can be a fixed or adjustable splitter plate, rotating drum, or conveyor. Some current designs also try to capture the lights fraction ‘superlights’ (plastic and paper) from the overall lights fraction that got previously blown over the gap by the initial air curtain, by means of additional suction air or a second air curtain in the area of the airborne superlights over the lights fraction. This method is marginally effective and makes the equipment much more complex to filter the air curtain air in an enclosed system, or collect and separate the air from super lights in an open system.
There are currently two styles of air classifiers, one that is open where the blower for the air curtain draws fresh air from outside the classifier and exhausts air, utilized for separating the heavy from the lights, out to atmosphere after the separation. The second style is an enclosed or closed system where the blower fan for the air curtain draws air from the a rear section of the unit where an expansion chamber collects the air which was utilized for the separation of rotatable permeable member. This enclosed or closed system will often have air filtration system that will continuously filter a recycled air and exhaust a portion of the recycled air to the atmosphere. This exhausted portion of is replaced with fresh air entering the system.
Materials separated by air classifiers typically do so by density separation of the materials through an air curtain or multiple curtains into two or possibly three fractions. Examples of the material to be separated are, for example, rock and aggregate as heavies which are separated from wood, plastic, paper as the lights; metals as heavies which are separated from plastics as lights; glass, metals and rock as heavies which are separated from paper, cardboard, and plastic as lights; rock as heavies which are separated from mulch or compost as lights; and mulch or compost as heavies which are separated from paper and plastic as lights. From each of the above lights fractions, it is desirable to segregate or separate the lights into both a light fraction and a super light fraction.